The present invention generally relates to vehicle brake systems, and more particularly relates to a device and a method for controlling an electrically actuated parking brake.
Parking brake systems are disclosed in the state of the art which are connected to a device that is activated by the physical strength of the driver by way of cables and linkage. The said muscular-power operated actuated device is typically a pedal activated by the driver""s foot or a hand brake lever activated by the driver""s hand.
Recently, parking brakes have become known wherein an electromotive brake actuation is provided. For example, DE 4129919 A1 describes that electric motors are arranged on the wheel brakes, respectively, and can be actuated by way of a corresponding signal so that the parking brake is activated.
However, the electrically actuated parking brake suffers from the disadvantage that the driver""s request is not taken into account appropriately (e.g. upon an actuation or activation of the parking brake, a maximum tensioning force would always be adjusted, with the result of excessive stress acting on the brake system at an early time.) This, in turn, would necessitate a more sophisticated construction of the parking brake system to withstand these stresses, which sophistication inevitably increases the price for its manufacture.
An object of the present invention is to provide a device and a method for controlling an electrically actuated parking brake which detect a driver""s request by way of an operating element and convert it into corresponding nominal values for the actuating force.
The present invention arranges for a device for actuation of an electrically actuated parking brake which may include input means for a driver""s request relating to an actuation of the parking brake. Further, the device of the present invention can comprise a control unit for detecting the driver""s request by way of a corresponding output signal of the input means. Still further, the control means can determine a nominal value FS_soll corresponding to the driver""s request and issue a control signal to an actuator of the parking brake corresponding to the determined nominal value FS_soll.
The solution according to the present invention permits converting the driver""s request directly into a corresponding nominal value FS_soll of the actuating force of the parking brake. The actuating force may roughly correspond to a tensioning force or a cable force. The actuator may be an electric motor which directly applies a brake shoe against a rotating part of the wheel brake. However, it is also possible that a Bowden cable is actuated by the electric motor or the actuator which will then actuate the wheel brake or the parking brake by way of corresponding deflection means.
The fact that a nominal value corresponding to the driver""s request is produced permits realizing a system which basically corresponds to that of the conventional, muscular-power operated parking brake. Thus, the driver hardly needs to adapt to a different way of braking because he/she is in a position to indicate by way of the input means a respective actuating force in conformity with his/her request. When the driver parks the vehicle e.g. on a flat underground, he/she is able to actuate the electrically actuated parking brake only to a slight degree according to his/her request. When the driver parks the vehicle on a steep downgrade, e.g. on a slope with a gradient of 30%, he/she may now adjust the maximum actuating force. Hence, the parking brake is loaded with the maximum actuating force only when this is absolutely necessary. Of course, this prolongs the service life of the brake system. Further, the driver may also use the parking brake according to the present invention as a hill holder on gradients when he/she chooses the actuating force to be low.
According to the present invention, the input means can be actuated by the driver to adopt a tensioning position, a release position, and a neutral position. Additionally, the input means can be designed as a tip switch, and the tip switch is redundant. This allows further enhancing the safety of actuation, and it is possible to detect potential defects.
When the input means has adopted a neutral position according to the present invention, an actual value FS_ist of the parking brake can be maintained. Once the input means has adopted the release position, the nominal value FS_soll is set to zero. When, in addition, the input means has adopted the tensioning position, the nominal value FS_soll will be increased starting from the actual value FS_ist.
The nominal value FS_soll can be increased gradually in a tensioning position until a limit value FS_max. It is, of course, also possible to infinitely variably increase the nominal value FS_soll, if desired.
It shall be noted in this respect that the above-mentioned example of the design of the input means as tip switch is meant as an option only. It is also feasible to provide a slider switch which indicates the nominal value FS_soll. Still other input means may be used, however, attention should be paid that the input means permits a haptic feedback. When the input means is actuated, this provides the driver with a feedback about which condition the parking brake is in right now and which nominal value is indicated at that moment.
Further, it is possible to represent the actual value FS_ist and/or the nominal value FS_soll by an optical display device. Such an optical display device could be light-emitting diodes or similar means that indicate to the driver which actuating force of the parking brake prevails at the moment or which actuating force of the parking brake is or was just input as nominal value by way of the input means.
Further, the control unit can induce an actuating electronics of the parking brake to switch to an inactive condition with a minimum power absorption upon expiry of a predetermined duration Trest after the last actuation of the input means. It is thereby possible to achieve a delay in disconnecting which switches the actuating electronics or the control unit into an operating mode with a minimum power absorption. It shall be noted in this respect that a separate control unit for the electrically actuated parking brake can be realized. However, it is also possible to integrate the control unit or the actuating electronics for the parking brake into an existing control unit, for example, into the control unit for the ABS brake system.